Experimental infection of bumble bees with honey bee associated viruses: no direct fitness costs but potential future threats to novel wild bee hosts

Pathogen spill-over represents an important cause of biodiversity decline. For wild bee species such as bumble bees, many of which are in decline, correlational data point toward viral spill-over from naged honey bees as a potential cause. Yet impacts of honey bee viruses on wild bees are rarely evaluated. Here, in a series of highly controlled laboratory infection assays with well characterised viral inocula, we show that three viral types isolated from honey bees (Deformed wing virus genotype A, Deformed wing virus genotype B and Black queen cell virus) readily replicate within hosts of the bumble bee Bombus terrestris. Impacts of these honey bee-derived viruses – either injected or fed – on the mortality of B. terrestris workers were, however, negligible and likely dependent on host condition. Our results highlight the potential threat of viral spill-over from honey bees to novel wild bee species, though they also underscore the importance of additional studies on this and other non-...